Exists query in Elasticsearch

Introduction

The Exists query helps you find documents that have a specific field filled in. It ignores documents where that field is missing.

You want to find all users who have provided their email address.

You want to list products that have a price set.

You want to filter blog posts that have an image attached.

You want to check which orders have a tracking number recorded.

Syntax

Elasticsearch

{
  "query": {
    "exists": {
      "field": "your_field_name"
    }
  }
}

Replace your_field_name with the exact name of the field you want to check.

This query returns documents where the field exists and is not null.

Examples

Finds all documents where the email field exists.

Elasticsearch

{
  "query": {
    "exists": {
      "field": "email"
    }
  }
}

Finds all documents where the price field exists.

Elasticsearch

{
  "query": {
    "exists": {
      "field": "price"
    }
  }
}

Sample Program

This query will return all documents that have a username field filled in.

Elasticsearch

{
  "query": {
    "exists": {
      "field": "username"
    }
  }
}

Important Notes

The exists query only checks if the field is present and not null.

If a field is an empty string or empty array, it still counts as existing.

Summary

The Exists query finds documents with a specific field present.

Use it to filter out documents missing important information.

It is simple and useful for many search filters.

Practice

1. What does the exists query do in Elasticsearch?

easy

A. Finds documents where a specific field is present

B. Finds documents where a field has a specific value

C. Deletes documents missing a field

D. Updates documents with a missing field

Solution

1. Step 1: Understand the purpose of the exists query

   The exists query checks if a field exists in documents, filtering those that have the field.

2. Step 2: Compare options with the query's function

   Only Finds documents where a specific field is present correctly describes this behavior; others describe different operations.

3. Final Answer:

   Finds documents where a specific field is present -> Option A

4. Quick Check:

   Exists query = finds documents with field [OK]

Hint: Exists query checks if a field is present in documents [OK]

Common Mistakes:

• Confusing exists query with term query
• Thinking it deletes or updates documents
• Assuming it checks field values

2. Which of the following is the correct syntax for an exists query in Elasticsearch?

easy

A. {"query": {"exists": {"field_name": "user"}}}

B. {"query": {"exists": "user"}}

C. {"query": {"exists": {"value": "user"}}}

D. {"query": {"exists": {"field": "user"}}}

Solution

1. Step 1: Recall the correct JSON structure for exists query

   The exists query requires a "field" key inside its object specifying the field name.

2. Step 2: Match options to correct syntax

   {"query": {"exists": {"field": "user"}}} matches the correct syntax: {"exists": {"field": "user"}}. Others use wrong keys or structure.

3. Final Answer:

   {"query": {"exists": {"field": "user"}}} -> Option D

4. Quick Check:

   Exists query syntax uses "field" key [OK]

Hint: Exists query needs "field" key inside its object [OK]

Common Mistakes:

• Using "value" or "field_name" instead of "field"
• Omitting the object braces around field
• Passing field as a string directly

3. Given the following Elasticsearch query, what documents will it return?

{"query": {"exists": {"field": "email"}}}

medium

A. Documents where the email field exists

B. Documents where the email field is missing

C. Documents where the email field is empty

D. All documents regardless of email field

Solution

1. Step 1: Analyze the query structure

   The query uses an exists query on the field "email", which filters documents having that field.

2. Step 2: Understand what exists means for documents

   Documents returned must have the "email" field present, regardless of its value.

3. Final Answer:

   Documents where the email field exists -> Option A

4. Quick Check:

   Exists query returns docs with field present [OK]

Hint: Exists query returns docs with the field present only [OK]

Common Mistakes:

• Thinking it returns docs missing the field
• Assuming empty fields are excluded
• Believing it returns all documents

4. Identify the error in this Elasticsearch exists query:

{"query": {"exists": {"field_name": "status"}}}

medium

A. The field value should be an array, not a string

B. The query should use "match" instead of "exists"

C. The key should be "field", not "field_name"

D. The query is missing a "filter" wrapper

Solution

1. Step 1: Check the key used inside exists query

   The exists query requires the key "field" to specify the field name.

2. Step 2: Compare the given key with the correct one

   The query uses "field_name" which is incorrect and causes an error.

3. Final Answer:

   The key should be "field", not "field_name" -> Option C

4. Quick Check:

   Exists query key = "field" [OK]

Hint: Use "field" key inside exists query, not "field_name" [OK]

Common Mistakes:

• Using incorrect key names inside exists query
• Confusing exists with match query
• Adding unnecessary wrappers

5. You want to find all documents where the field phone exists but is not empty or null. Which Elasticsearch query best achieves this?

hard

A. {"query": {"bool": {"must": [{"exists": {"field": "phone"}}, {"term": {"phone": ""}}]}}}

B. {"query": {"bool": {"must": [{"exists": {"field": "phone"}}, {"script": {"script": "doc['phone'].value != ''"}}]}}}

C. {"query": {"exists": {"field": "phone"}}}

D. {"query": {"exists": {"field": "phone"}, "term": {"phone": ""}}}

Solution

1. Step 1: Understand the requirement

   We want documents where "phone" exists and is not empty or null.

2. Step 2: Evaluate each option

   {"query": {"exists": {"field": "phone"}}} only checks existence, not emptiness. {"query": {"bool": {"must": [{"exists": {"field": "phone"}}, {"term": {"phone": ""}}]}}} incorrectly requires phone to be empty. {"query": {"exists": {"field": "phone"}, "term": {"phone": ""}}} has invalid syntax combining exists and term at same level. {"query": {"bool": {"must": [{"exists": {"field": "phone"}}, {"script": {"script": "doc['phone'].value != ''"}}]}}} uses a bool must with exists and a script checking phone is not empty, correctly filtering as needed.

3. Final Answer:

   {"query": {"bool": {"must": [{"exists": {"field": "phone"}}, {"script": {"script": "doc['phone'].value != ''"}}]}}} -> Option B

4. Quick Check:

   Exists + script to exclude empty = {"query": {"bool": {"must": [{"exists": {"field": "phone"}}, {"script": {"script": "doc['phone'].value != ''"}}]}}} [OK]

Hint: Combine exists with script to exclude empty values [OK]

Common Mistakes:

• Using exists alone without checking empty values
• Incorrectly combining queries at same level
• Assuming term query with empty string works for exclusion